Lubricating oil composition for internal combustion engines

ABSTRACT

Provided is a lubricant oil composition for an internal combustion engine which is characterized by including a base oil having a viscosity index of 125 or higher and a Noack evaporation amount (250° C.×1 h) of 15% by mass or less, and, based on a total amount of the composition, from 0.1 to 10% by mass of (A) a C 2  to C 20  olefin polymer having a mass average molecular weight of 500 or more and 10,000 or less and/or (B) a polymeric compound having a mass average molecular weight of 10,000 or more and less than 100,000, wherein a content of (C) a polymeric compound having a mass average molecular weight of 100,000 or more is less than 1.0% by mass. The lubricant oil composition can, despite of its low viscosity, reduce noise during running, prevent fatigue damage such as gear pitting, reduce the consumption of the oil, and provide excellent fuel saving performance.

TECHNICAL FIELD

The present invention relates to a lubricant oil composition for internal combustion engines and, more specifically, to a lubricant oil composition for internal combustion engines which can reduce noise during running, improve fatigue life, reduce lubricating oil consumption and provide excellent fuel saving performance and which is useful as a lubricating oil for four-cycle engines for motorcycles.

BACKGROUND ART

Because of demand for energy saving and reduction of carbon dioxide (CO₂), fuel saving performance is strongly desired in the field of lubricating oils for internal combustion engines (engine oils) as one of required properties thereof.

In the case of engine oils for automobiles, it has been a conventional practice to reduce the viscosity thereof for the purpose of improving their fuel saving performance.

In the case of engine oils for motorcycles, however, various problems arise, when the viscosity thereof is reduced to improve the fuel saving performance thereof although both are equally called engine oils, due to differences in mechanical structure between automobiles and motorcycles.

Namely, since devices such as an engine of the motorcycles are required to have a compact size, motorcycles have a structure in which the same engine oil is commonly used for lubricating the engine as well as the transmission.

When an engine oil, whose viscosity has been reduced in order to improve fuel saving performance, is used in a motorcycle having the above structure, fatigue damage such as gear pitting is caused in a transmission thereof. Additionally, in the motorcycle, since the engine is installed in an exposed state, engine noise is big to cause noise pollution problems. Moreover, since the engine of the motorcycle is small in size, the temperature of the oil becomes higher as compared with that of automobiles. It follows that oil consumption is increased due to oil evaporation.

Therefore, it is necessary to solve these problems when the fuel saving performance of the engine oil for use in motorcycles is attempted to be improved by reducing the viscosity thereof.

As a method for reducing the viscosity in an actually employed temperature range, an attempt has been hitherto made to improve the viscosity index by using a base oil in combination with a viscosity index improver that is a polymeric compound (see, for example, Patent Document 1). A lubricating oil containing the viscosity index improver, however, causes a reduction of its viscosity due to orientation of the polymer molecules when the oil is subjected to high shear conditions such as by bearings or gear teeth of the engine. Thus, because the conventional multi-grade engine oil (lubricating oil containing a polymeric compound) cannot maintain sufficient high temperature high shear viscosity, the metal fatigue resistance thereof tends to be reduced. This is an obstacle against reduction of the viscosity of engine oils for motorcycles.

Therefore, the foregoing problems, encountered when the viscosity of an engine oil for use in motorcycles is reduced so as to improve the fuel saving performance thereof, have not yet been solved at present.

PRIOR ART DOCUMENT Patent Document Patent Document 1: JP2000-087070A SUMMARY OF THE INVENTION Problems to be Solved by the Invention

With the foregoing circumstance in view, it is an object of the present invention to provide a lubricant oil composition for internal combustion engines which can, despite of its low viscosity, reduce noise during running, prevent fatigue damage such as gear pitting, reduce the consumption of the oil and provide excellent fuel saving performance.

Means for Solving the Problem

The present inventors have made an earnest study and, as a result, found that the above object can be achieved by blending a specific base oil with a polymer having a specific structure and molecular weight and/or a polymeric compound having a specific molecular weight. The present invention has been completed based on such a finding. Thus, the present invention provides:

[1] A lubricant oil composition for an internal combustion engine, comprising: a base oil having a viscosity index of 125 or higher and a Noack evaporation amount (250° C.×1 h) of 15% by mass or less, and, based on a total amount of the composition, from 0.1 to 10% bymass of (A) a C2 to C₂₀ olefin polymer having amass average molecular weight of 500 or more and 10,000 or less and/or (3) a polymeric compound having a mass average molecular weight of 10,000 or more and less than 100,000, wherein a content of (C) a polymeric compound having a mass average molecular weight of 100,000 or more is less than 1.0% by mass; [2] The lubricant oil composition for an internal combustion engine according to above [1], wherein the polymeric compound is one or two or more selected from polymethacrylates, olefin copolymers, styrene copolymers and polyisobutylenes; [3] The lubricant oil composition for an internal combustion engine according to above [1] or [2], further comprising a molybdenum-based friction modifier or an ashless friction modifier; [4] The lubricant oil composition for an internal combustion engine according to any one of above [1] to [3], wherein the Noack evaporation amount (250° C.×1 h) is 10.0% by mass or less and the viscosity index is 140 or higher; and [5] The lubricant oil composition for an internal combustion engine according to any one of above [1] to [4], wherein the lubricant oil composition is used for a four-cycle engine for a motorcycle.

Effect of the Invention

According to the present invention, it is possible to provide a lubricant oil composition for internal combustion engines which can, despite of its low viscosity, reduce noise during running, prevent fatigue damage such as gear pitting, reduce the consumption of the oil and provide excellent fuel saving performance.

Embodiments of the Invention

The lubricant oil composition for internal combustion engines (hereinafter occasionally referred to simply as “the present composition”) is characterized by containing a base oil having a viscosity index of 125 or higher and a Noack evaporation amount (250° C.×1 h) of 15% by mass or less, and, based on a total amount of the composition, from 0.1 to 10% by mass of (A) a C₂ to C₂₀ olefin polymer having a mass average molecular weight of 500 or more and 10,000 or less and/or (B) a polymeric compound having a mass average molecular weight of 10,000 or more and less than 100,000, wherein a content of (C) a polymeric compound having a mass average molecular weight of 100,000 or more is less than 1.0% by mass. The present composition will be next described in detail below.

1. Base Oil:

The base oil used in the present invention is a lubricating base oil formed of a mineral oil, a synthetic oil or a mixture thereof and must have a viscosity index of 125 or more. As the viscosity index of the base oil is higher, the viscosity of the lubricant oil composition for internal combustion engines at high temperatures may be prevented from decreasing so that the wear resistance and fatigue life thereof can be prevented from decreasing.

The viscosity index is preferably 130 or more. The viscosity index as used herein is as measured according to JIS K 2283.

The base oil used in the present invention must also have a Noack evaporation amount (250° C.×1 h) of 15% by mass or less. When the Noack evaporation amount (250° C.×1 h) exceeds 15% by mass, the consumption of the oil increases due to the evaporation loss of the present composition. The Noack evaporation amount is preferably 10% by mass or less.

As used herein, the Noack evaporation amount is as measured according to CEC-L-40-A-93, ASTM D5800.

It is also preferred that the base oil have a % C_(A) of 3.0 or less as measured by ring analysis and a sulfur content of 100 ppm by mass or less.

As used herein, the term “% C_(A) as measured by ring analysis” means a proportion (percentage) of an aromatic component which is calculated by the n-d-M ring analysis method. The sulfur content as used herein means the value as measured according to JIS K 2541.

The base oil having a % C_(A) of 3.0 or less and a sulfur content of 100 ppm by mass or less exhibits good oxidation stability and can give a lubricant oil composition that can suppress an increase of the acid value and formation of a sludge. The % C_(A) of the base oil is more preferably 1.0 or less, still more preferably 0.5 or less.

The base oil used in the present composition preferably has a kinematic viscosity at 100° C. of 2 to 20 mm²/s, more preferably 3 to 15 mm²/s, still more preferably 3.5 to 10 mm²/s. When the kinematic viscosity of the base oil is excessively high, the stirring resistance of the obtained composition is increased. In addition, because the friction coefficient in fluid lubrication region is increased, the fuel saving performance is deteriorated. When the kinematic viscosity is excessively low, on the other hand, wear is increased in sliding parts, such as a valve operating system, pistons, rings and bearings, of an internal combustion engine.

Examples of the mineral oils include those which are obtained by subjecting a lube-oil distillate (which is obtained by atmospheric distillation of a crude oil or by vacuum distillation of an atmospheric residue) to one or more refining treatments such as solvent deasphalting, solvent extraction, solvent dewaxing, catalytic dewaxing, hydrorefining and hydrocracking, and those which are produced by isomerizing mineral oil-based waxes or waxes (GTL waxes) manufactured by, for example, Fischer Torpsh process.

The base oil having the viscosity index of 125 or more used in the present invention may be particularly preferably produced by solvent-dewaxing or hydrodewaxing of a product oil that is obtainable by hydrocracking of lube oil distillates or hydroisomerization of waxes.

The hydrocracking may be carried out by contacting a lube oil distillate with a hydrocracking catalyst (for example, a catalyst containing at least one of Group 8 metals such as nickel and cobalt and at least one of Group 6A metals such as molybdenum and tungsten which metals are supported on a silica-alumina carrier) at a temperature of 350 to 450° C. and LHSV (liquid space velocity) of 0.1 to 2 hours⁻¹ in the presence of hydrogen having a hydrogen partial pressure of 7 to 14 MPa.

The hydroisomerization of wax may be carried out, for example, by contacting a slack wax, obtained by solvent dewaxing of a mineral oil-based lubricating oil or a wax obtained by Fischer Torpsh synthesis, with a hydroisomerization catalyst (for example, a catalyst formed by supporting at least one of Group 8 metals such as nickel and cobalt and Group 6A metals such as molybdenum and tungsten on an alumina carrier or a silica-alumina carrier, a zeolite catalyst or a catalyst formed by supporting platinum and the like on a zeolite-containing carrier) at a temperature of 300 to 450° C. and LHSV (liquid-space velocity) of 0.1 to 2 hours⁻¹ in the presence of hydrogen having a hydrogen partial pressure of 5 to 14 MPa.

The hydrocracking product oil and hydroisomerization product oil obtained by the above processes are generally each subjected to distillation to remove a light fraction and to obtain a lube oil fraction. A lubricating base oil having a low pour point (for example, −10° C. or less) maybe obtained by further dewaxing the lube oil fraction to remove wax therefrom.

If desired, the lube oil fraction obtained by the above process may be further subjected to a solvent refining or hydrorefining treatment.

As the synthetic oil, a variety of conventionally known synthetic oils may be used. For example, there may be used poly-α-olefin, polybutene, polyol esters, dibasic acid esters, aromatic esters, phosphoric acid esters, polyphenyl ethers, alkylbenzenes, alkylnaphthalenes, polyoxyalkylene glycol, neopentyl glycol, silicone oil, trimethylolpropane, pentaerythritol and hindered esters. Above all poly-α-olefin is particularly preferred for reasons that it has relatively a high viscosity index, that it has similarity to a mineral oil in composition and that it permits the use of additives employed in the conventionally mineral oils.

The base oil used in the present invention may be a mixture of two or more types of mineral oils, a mixture of two or more types of synthetic oils, or a mixture of a mineral oil and a synthetic oil, as long as the above properties are satisfied. A mixing ratio of two or more types of base oils in the mixture may be selected arbitrarily.

2. Olefin Polymer and Polymeric Compound:

The lubricant oil composition for internal combustion engines according to the present invention is obtainable by blending the above-described base oil with 0.1 to 10% by mass, preferably 0.3 to 7% by mass, more preferably 0.5 to 5% by mass, of (A) a C₂ to C20 olefin polymer having a mass average molecular weight of 500 or more and 10,000 or less and/or (B) a polymeric compound having a mass average molecular weight of 10,000 or more and less than 100,000, wherein a content of (C) a polymeric compound having a mass average molecular weight of 100,000 or more is less than 1.0% by mass.

By blending the C₂ to C₂₀ olefin polymer having a mass average molecular weight of 500 or more and 10,000 or less and/or the polymeric compound having a mass average molecular weight of 10,000 or more and less than 100,000, it is not only possible to increase the viscosity index of the composition but also to prevent generation of noises.

The mass average molecular weight of (B) the polymeric compound to be mixed to the base oil is adjusted to be less than 100,000. This is because, although the viscosity index is more improved by increasing the molecular weight of the polymeric compound to be mixed to the base oil, there is a possibility that molecular chains of the polymeric compound are oriented when subjected to shear so that the viscosity may temporary decrease, whereby the required high-temperature high-shear viscosity may not be maintained. There is an additional possibility that the molecular chains of the polymeric compound may be cut during use so that the molecular weight decreases to cause a decrease in viscosity.

Accordingly, it is desirable that (C) the polymer compound having a mass average molecular weight of 100,000 or more (preferably 70,000 or more, more preferably 50,000 or more) be not contained. However, there may arise cases in which such a polymeric compound is unavoidably added in order to improve the viscosity index. Even in such cases, the amount of such a polymeric compound is suppressed below less than 1.0% by mass, preferably 0.1% by mass, more preferably 0.01% by mass in order to obtain the lubricant oil composition for the internal combustion engines according to the present invention.

The mass average molecular weight of (B) the polymeric compound is preferably 70,000 or less, more preferably 50,000 or less.

As (A) the olefin polymer, at least one selected from homopolymers and copolymers of a C₂ to C₂₀, preferably C₂ to C16, more preferably C₂ to C₁₄ olefin is used. Typical examples of the C₂ to C20 olefin polymer include ethylene-α-olefin copolymers, and homopolymers and copolymers of an α-olefin. As the ethylene-α-olefin copolymer, there may be mentioned copolymers of 15 to 80 mole % of ethylene with a C₃ to C₂₀ α-olefin such as propylene, 1-butene or 1-decene. These copolymers may be random copolymers or block copolymers. These copolymers are of a non-dispersible in a lubricating oil. However, dispersible copolymers that are obtained by grafting maleic acid, N-vinylpyrrolidone, N-vinylimidazole, glycidyl acrylate or the like onto the ethylene-α-olefin copolymers may be also used. As the homopolymers and copolymers of an a-olefin, there may be used homopolymers and copolymers of a C₄ to C₂₀, preferably C₆ to C₁₆, more preferably C₆ to C₁₄ α-olefin. The copolymers may be random or block copolymers.

These ole fin polymers maybe produced by any method; for example by thermal reaction using no catalyst. Additionally, the olefin polymers may be produced by homopolymerizing or copolymerizing the above-described olefin using known catalyst systems such as organic peroxide catalysts, e.g. benzoyl peroxide; Friedel Kraft catalysts, e.g. aluminum chloride, aluminum chloride-polyhydric alcohol system, aluminum chloride-titanium tetrachloride system, aluminum chloride-alkyltin halide system and boron fluoride; Ziegler catalysts, e.g. organoaluminum chloride-titanium tetrachloride system and organoaluminum-titanium tetrachloride system; metallocene catalysts, e.g. aluminoxane-zirconocene system and ionic compound-zirconocene system; and Lewis acid-complex catalysts, e.g. aluminum chloride-base system and boron fluoride-base system. While the above exemplified olefin polymers may be used as such, it is preferable to use hydrogenated products obtained by hydrogenating double bonds of the olefin polymers.

The mass average molecular weight of the olefin polymer is preferably 2,000 to 9,000, more preferably 3,000 to 8,000.

As the above-described polymeric compound, there may be preferably mentioned at least one selected from polymethacrylates (PMA), olefin copolymers, styrene copolymers (e.g. hydrogenated styrene-diene copolymers) and polyisobutylene. The polymethacrylates may be of a dispersible or non-dispersible type. An ethylene-α-olefin copolymer is the representative of the olefin copolymers.

One of these polymeric compounds may be used alone, or two or more thereof may be used in combination. Polymethacrylates (PMA) and olefin copolymers are more preferable.

3. Friction Modifier

In the lubricating oil composition for internal combustion engines according to the present invention, it is preferred that a molybdenum-based friction modifier or an ashless frictionmodifier be used in order to improve the fuel saving performance. Use of the molybdenum-based friction modifier and the ashless friction modifier in combination is more preferable.

As the molybdenum-based friction modifier, there may be preferably used at least one selected from molybdenum dithiocarbamate (MoDTC), molybdenum dithiophosphate (hereinafter occasionally referred to as MoDTP) and an amine salt of molybdic acid (hereinafter occasionally referred to as Mo amine salt) . Among the molybdenum-based friction modifiers, MoDTC is preferred for reasons of its effectiveness. One of the molybdenum-based friction modifiers may be used alone, or two or more thereof may be used in combination. The molybdenum based modifier is preferably used in an amount of 10 to 1,000 ppm by mass, more preferably 100 to 800 ppm by mass, in terms of molybdenum, based on the total amount of the composition. When the amount of molybdenum is less than 10 mass ppm, friction reduction is not sufficiently obtained. When the amount of molybdenum exceeds than 1,000 ppm by mass, improvement in friction property obtained is not in proportion to the amount thereof.

MoDTC is represented by the general formula (I) below.

In the general formula (I), R¹ to R⁴, which may be the same or different, each represent a C₅ to C₁₆ hydrocarbon group . X represents S (sulfur atom) or O (oxygen atom). Examples of the hydrocarbon group represented by R¹ to R⁴ are C₅ to C16 alkyl groups, C₅ to C₁₆ alkenyl groups, C₅ to C₁₆ cycloalkyl groups, C₅ to C₁₆ alkylaryl groups and C₅ to C₁₆ arylalkyl groups. Specific examples of the C₅ to C₁₆ hydrocarbon include various pentyl groups, various hexyl groups, various heptyl groups, various octyl groups, various nonyl groups, various decyl groups, various undecyl groups, various dodecyl groups, various tridecyl groups, various tetradecyl groups, various pentadecyl groups, various hexadecyl groups, various octenyl groups, various nonenyl groups, various decenyl groups, various undecenyl groups, various dodecenyl groups, various tridecenyl groups, various tetradecenyl group, various pentadecenyl groups, a cyclohexyl group, a dimethylcyclohexyl group, an ethylcyclohexyl group, a methylcyclohexylmethyl group, a cyclohexylethyl group, a propylcyclohexyl group, a butylcyclohexyl group, a heptylcyclohexyl group, a phenyl group, a tolyl group, a dimethylphenyl group, a butylphenyl group, a nonylphenyl group, a methylbenzyl group, a phenylethyl group, a naphthyl group and a dimethylnaphthyl group.

MoDTP is represented by the general formula (II) below.

In the formula (II), R⁵ to R⁸, which may be the same or different, each represent a C₅ to C₁₆ hydrocarbon group. Y represents S (sulfur atom) or O (oxygen atom). Examples of the hydrocarbon group represented by R⁵ to R⁸ are C₅ to C1₆ alkyl groups, C₅ to C₁₆ alkenyl groups, C₅ to C₁₆ cycloalkyl groups, C₅ to C₁₆ alkylaryl groups and C₅ to C₁₆ arylalkyl groups. Specific examples of the C₅ to C₁₆ hydrocarbon include various pentyl groups, various hexyl groups, various heptyl groups, various octyl groups, various nonyl groups, various decyl groups, various undecyl groups, various dodecyl groups, various tridecyl groups, various tetradecyl groups, various pentadecyl groups, various hexadecyl groups, various octenyl groups, various nonenyl groups, various decenyl groups, various undecenyl groups, various dodecenyl groups, various tridecenyl groups, various tetradecenyl group, various pentadecenyl groups, a cyclohexyl group, a dimethylcyclohexyl group, an ethylcyclohexyl group, a methylcyclohexylmethyl group, a cyclohexylethyl group, a propylcyclohexyl group, a butylcyclohexyl group, a heptylcyclohexyl group, a phenyl group, a tolyl group, a dimethylphenyl group, a butylphenyl group, a nonylphenyl group, a methylbenzyl group, a phenylethyl group, a naphthyl group and a dimethylnaphthyl group.

The Mo amine salt is a secondary amine salt of molybdic acid represented by the general formula (III) below.

In the general formula (III), R represents a C₅ to C18 hydrocarbon group. The four hydrocarbon groups may be the same or different. Examples of the C₅ to C₁₈ hydrocarbon group include C₅ to C18 alkyl groups, C₅ to C₁₈ alkenyl groups, C₅ to C₁₈ cycloalkyl groups, C₅ to C₁₈ alkylaryl groups and C₅ to C₁₈ arylalkyl groups. Specific examples of the C₅ to C₁₈ hydrocarbon include various pentyl groups, various hexyl groups, various heptyl groups, various octyl groups, various nonyl groups, various decyl groups, various undecyl groups, various dodecyl groups, various tridecyl groups, various tetradecyl groups, various pentadecyl groups, various hexadecyl groups, various heptadecyl, various octadecyl groups, various octenyl groups, various nonenyl groups, various decenyl groups, various undecenyl groups, various dodecenyl groups, various tridecenyl groups, various tetradecenyl group, various pentadecenyl groups, a cyclohexyl group, a dimethylcyclohexyl group, an ethylcyclohexyl group, a methylcyclohexylmethyl group, a cyclohexylethyl group, a propylcyclohexyl group, a butylcyclohexyl group, a heptylcyclohexyl group, a phenyl group, a tolyl group, a dimethylphenyl group, a butylphenyl group, a nonylphenyl group, a methylbenzyl group, a phenylethyl group, a naphthyl group and a dimethylnaphthyl group.

Examples of the ashless friction modifier include fatty acids, higher alcohols, fatty acid esters, oils and fats, amines, amides and ester sulfides. These friction modifiers may be used singly or in combination of a two or more thereof. The modifier is generally used in an amount of 0.01 to 10% by mass based on the total amount of the composition.

4. Lubricant Oil Composition for Internal Combustion Engine

The lubricant oil composition for internal combustion engine according to the present invention may be obtained by adjusting the viscosity index and Noack evaporation amount (250° C.×1 h) of the base oil, the mass average molecular weight of each of the olefin polymer and polymeric compound, and the blending amount of the polymeric compound in the above defined ranges. By so doing, it is possible to obtain a lubricant oil composition for internal combustion engines of a fuel saving type which has a viscosity index of 135 or more or 140 or more, which can reduce noises and which has excellent effect of preventing fatigue damage such as gear pitting.

It is preferred that the viscosity reduction rate of the present composition at a high shear and at 150° C. be 3.0% or less relative to the viscosity at a low shear. This is because, when the viscosity reducing rate at a high shear of a lubricating oil for internal combustion engines exceeds 3.0%, it is necessary that the viscosity thereof at a low shear be set at a high level in expectation of the reduction of the viscosity. This inevitably results in deterioration of the fuel saving performance.

It is further preferred that the lubricant oil composition have a kinematic viscosity at 100° C. of less than 11.0 mm²/s. When the kinematic viscosity is beyond 11.0 mm²/s, the kinematic viscosity in a temperature range (80 to 100° C.) during actual use of the lubricating oil for internal combustion engines becomes so high that it is not possible to achieve fuel saving.

It is particularly preferred that the lubricant oil composition have a kinematic viscosity at 100° C. of less than 9.0 mm²/s, when its high-shear viscosity at 150° C. is 2.9 mPa·s or more (equivalent to SAE viscosity grade of 30). When the high-shear viscosity at 150° C. of the lubricant oil composition is 2. 6mPa·s or more (equivalent to SAE viscosity grade of 20), it is preferred that the lubricant oil composition have a kinematic viscosity at 100° C. of less than 7.5 mm²/s. When the kinematic viscosity at 100° C. exceeds the above upper limit, the viscosity of the lubricating oil for internal combustion engines in the practically employed temperature range (80 to 100° C.) becomes so high that it is not possible to achieve better fuel saving as compared with the conventional oil.

5. Other Additives

Further, into the lubricant oil composition for internal combustion engines according to the present invention, various additives represented by an ashless dispersant, a metal detergent, an extreme pressure agent, a metal deactivator, a rust inhibitor, an antifoaming agent, an anti-emulsifier and a coloring agent may blended singly or in combination of two or more thereof, as long as the object of the invention is not adversely affected.

Examples of the ashless dispersant include polybutenylsuccinimide, polybutenyl benzylamine, polybutenylamine and derivatives thereof (e.g. boric acid-modified products thereof) each having a polybutenyl group with a mass average molecular weight of 900 to 3,500. These ashless dispersants may be used singly or in combination of two or more thereof. The blending amount of the ashless dispersant is generally in the range of 0.01 to 10% by mass based on a total amount of the composition.

Examples of the metal detergent include alkali metal (such as sodium (Na) and potassium (K)) or alkaline earth metal (such as calcium (Ca) and magnesium (Mg)) sulfonates, phenates, salicylates and naphthenates. These metal detergents may be used singly or in combination of two or more thereof . A total base number and a blending amount of the metal detergent may be suitably selected depending on required properties of the lubricating oil. The total base number as measured by a perchloric acid method is generally in the range of 0 to 500 mg KOH/g, desirably 10 to 400 mg KOH/g. The blending amount is generally in the range of 0.1 to 10% by mass based on the total amount of the composition.

Examples of the extreme pressure agent include sulfur compounds such as olefin sulfides, dialkyl polysulfides, diarylalkyl polysulfides and diaryl polysulfides; phosphorous compounds such as phosphate esters, thiophosphate esters, phosphite esters, alkyl hydrogen phosphites, phosphate ester amine salts and phosphite ester amine salts. The blending amount of the extreme pressure agent is generally in the range of 0.01 to 10% by mass based on the total amount of the composition.

Examples of the metal deactivator include benzotriazole, triazole derivatives, benzotriazole derivatives and thiadiazole derivatives. The blending amount of the metal deactivator is generally in the range of 0.01 to 3% by mass based on the total amount of the composition.

Examples of the rust inhibitor include fatty acids; alkenylsuccinic acid half esters; fatty acid soaps; alkylsulfonic acid salts; alkaline earth metal (e.g. calcium (Ca), magnesium (Mg) and barium (Ba)) sulfonates, phenates, salicylates and naphthenates; fatty acid esters of polyhydric alcohols, fatty acid amines, oxidized paraffins and alkylpolyoxyethylene ethers. The blending amount of the rust inhibitor is generally in the range of 0.01 to 5% by mass based on the total amount of the composition.

As the antifoaming agent, a liquid silicone is suitably used. Illustrative of usable antifoaming agent are methylsilicone, fluorosilicone and polyacrylates. The blending amount of the antifoaming agent is preferably in the range of 0.0005 to 0.1% by mass based on the total amount of the composition.

As the anti-emulsifier there may be used ethylene-propylene block polymers; and alkali earth metal (e.g., calcium (Ca) and magnesium (Mg)) sulfonates, phenates, salicylates and naphthenates. The blending amount of the anti-emulsifier is generally in the range of 0.0005 to 1% by mass.

As the coloring agent, dyes and pigments may be used. The blending amount of the coloring agent is preferably in the range of 0.001 to 1% by mass based on the total amount of the composition.

Since the thus blended lubricant oil composition for internal combustion engines according to the present invention has the above described composition, there may be obtained the effects that evaporation loss is low, viscosity index is high and viscosity reduction rate at high temperature and high shear is small, despite of its low viscosity. In addition to such properties, the lubricant oil composition especially exhibits noise reducing effect, fatigue damage preventing effect, and fuel saving effect. Accordingly, the present composition may be suitably used as lubricating oil for internal combustion engines, in particular as lubricant oil composition for internal combustion engines that is useful as a lubricating oil for four-cycle engines for motorcycles.

EXAMPLES

The present invention will be next described in more detail by way of Examples. The present invention, however, is not limited to these examples in any way.

The properties of the lubricant oil compositions (sample oils) in each of the examples are measured by the following methods.

(1) Kinematic Viscosity (at 40° C. and 100° C.) and Viscosity Index:

Measured according to a method of JIS K 2283.

(2) HTHS Viscosity (at 150° C.):

Measured according to a method of ASTM D4683 using a TBS (Tapered Bearing Simulator) high temperature viscometer. Testing conditions are as follows:

Shear Rate: 10⁶sec⁻¹

Rotation Speed (motor): 3000 rpm

Space (Rotor/Stator): 2 to 3 μm

Sample Amount: 20 to 50 ml

Measurement Time: 4 to 6 hours for correction and 15 minutes for testing

(3) Viscosity at Low Temperature (CCS Viscosity):

Viscosity at −25° C. and at −30° C. was measured according to JIS K2606.

(4) Noack Evaporation Amount:

Evaporation amount was measured according to a method as specified in CEC-L-40-A-93 and ASTM D5800/A. The test condition is at 250° C. for 1 hour.

(5)Evaluation of Noise

Noise generated in an engine motoring apparatus shown below and operated under the conditions shown below was measured by the method shown below.

Engine-Motoring Tester and Engine Operating Condition:

Engine: Water-cooled 600 cc 4-cylinder engine for motorcycle Electric motor for driving the engine: 7.5 kW Valve style: DOHC (direct acting type) Engine speed: 3,000 rpm Oil temperature in the oil pan: 100° C.

Method for Measuring Noise:

Using a noise meter (LA5560, manufactured by ONO SOKKI Co., Ltd.), a power spectrum at a frequency of 6,300 Hz was measured by a frequency analyzer (REPOLYZER XN-8100, manufactured by ONO SOKKI Co., Ltd.).

(6) Evaluation of Property for Fuel Saving Performance

An engine oil was filled into an engine having the specification shown below for carrying out motoring torque test. Torque (dB) was measured at a predetermined engine revolution number. Test conditions are as follows.

Engine-motoring tester and engine operation condition: Engine: Water-cooled 600 cc 4-cylinder engine for motorcycle Valve style: DOHC (direct acting type) Engine speed: 5,000 rpm

Oil temperature in the oil pan: 100° C.

Electric motor for driving the engine: 7.5 kW

(7) Fatigue Life

A fatigue life was measured with a four-ball rolling fatigue tester in the following manner.

Bearing:

Material: bearing steel

Test piece: 60 mm diameter×5 mm thick

Testing steel ball dimensions: ⅜ inch diameter

Test Conditions:

Load: 147 N

Rotational speed: 2,200 rpm

Oil temperature: 120° C.

Evaluation Method:

A time period required until flaking took place in the test piece was defined as a fatigue life. The results of the test repeated six times were subjected to Weibull statistical analysis to calculate an L50 (minute).

(8) Viscosity Reduction Rate

A low shear viscosity at 150° C. was calculated by multiplying a value of the kinetic viscosity at 150° C., which was obtained from the kinematic viscosity and viscosity index at 100° C., by a value of the density at 150° C., which was obtained by extrapolation from the density at 15° C. and the density at 80° C. measured according to JIS K2249. A viscosity reduction rate was calculated from the obtained value of the low shear viscosity and the above-described HTHS viscosity (150° C.)

Examples 1 to 5 and Comparative Examples 1 to 7

Lubricant oil compositions for internal combustion engines (sample oils) were prepared according to formulations shown in Table 1 using various base oils and various copolymers, polymeric compounds and additives shown below. The prepared sample oils were evaluated for their various properties according to the above-described methods. The results are shown in Table 1.

<Base Oil>

Base Oil-1: Mineral oil-based hydrocracked base oil (API classification of GIII), 100N, Kinematic viscosity at 100° C. of 4.175 mm²/s; Viscosity Index of 130, Sulfur content of 0.01% by mass or less, % C_(A) of 0, Noack evaporation amount of 14% by mass; Base Oil-2: Mineral oil-based hydrocracked base oil (API classification of GIII), 150N, Kinematic viscosity at 100° C. of 6.274 mm²/s; Viscosity Index of 129, Sulfur content of 0.01% by mass or less, % C_(A) of 0, Noack evaporation amount of 6% by mass; Base Oil-3: Mineral oil-based hydrorefined base oil (API classification of GII), 150N, Kinematic viscosity at 100° C. of 5.284 mm²/s; Viscosity Index of 104, Sulfur content of 0.01% by mass or less, % C_(A) of 0, Noack evaporation amount of 14% by mass; Base Oil-4: Mineral oil-based hydrorefined base oil (API classification of GII), 500N, Kinematic viscosity at 100° C. of 10.89 ram²/s; Viscosity Index of 107, Sulfur content of 0.01% by mass or less, % C_(A) of 0, Noack evaporation amount of 4% by mass; Base Oil-5: Mineral oil-based hydrorefined base oil (API classification of GII), Bright stock, API classification of GII, Kinematic viscosity at 100° C. of 30.86 mm²/s; Viscosity Index of 107, Sulfur content of 0.01% by mass or less, % C_(A) of 0, Noack evaporation amount of 2% by mass or less.

<Olefin Polymer>

Copolymer-1: Ethylene-α-olefin copolymer, Mass average molecular weight of 4,700 (LUCANT HC600 manufactured by Mitsui Chemicals, Inc.);

<Polymeric Compound>

Copolymer-2: Ethylene-α-olefin copolymer, Mass average molecular weight of 7,000 (LUCANT HC2000 manufactured by Mitsui Chemicals, Inc.); Polymeric compound-1: Polymethacrylate (PMA), Mass average molecular weight of 45,000 (ACLUBE C-728 manufactured by Sanyo Chemical Industries, Ltd.); Polymeric compound-2: Olefincopolymer (OCP), Mass average molecular weight of 100,000 (Paratone 8057 manufactured by Chevron Corporation).

<Pour Point Depressant>

PMA, Mass average molecular weight of 690,000 (PLEXOL-162 manufactured by Degussa GmbH).

<Friction Modifier>

Molybdenum-based friction modifier: Molybdenum dialkyldithiocarbamate was used as a molybdenum friction modifier. The molybdenum content was 4.5% by weight.

<DI Agent>

Package additive: Mixture of ZnDTP (1.1), metal detergent (4), boron-modified succinimide A (1), boron-modified succinimide B (1), polybutenylsuccinimide (2.1), amine-based antioxidant (0.8) and diluent (balance). Numerals within parentheses denote contents in terms of % by mass.

TABLE 1 Example 1 2 3 4 5 SAE Viscosity Classification of Composition 5W-20 5W-20 10W-20 10W-30 5W-20 Composition Base Oil Base Oil-1 38   38   (% by mass) Base Oil-2 50.7 88.7 87.7 86.2 50   Base Oil-3 Base Oil-4 Base Oil-5 Copolymer Copolymer-1 2  1.5 Copolymer-2 1  1  Polymeric Polymeric Compound-1 1 2 Compound Polymeric Compound-2 Additive Pour Point Depressant  0.3 0.3  0.3 0.3  0.3 Friction Modifier  0.7 DI Agent 10   10 10   10 10   Property of Viscosity Index — — 133   129 129   129 133   Base oil Noack Evaporation 250° C. × 1 h % by mass  8.4 6 6  6 8  Amount Performance Kinematic  40° C. mm²/s 43.5 46.18  52.03 63.52 43.8 and Property Viscosity 100° C.  7.64 7.854   8.597 10.55  7.68 of Viscosity Index — — 145   140 142   156 145   Composition HTHS Viscosity 150° C. mPa · s  2.6 2.6  2.9 3.5  2.6 Viscosity Reduction 150° C. %  1> 1  1> 1  1> Percentage CCS Viscosity −25° C. mPa · s — — 4400    5400 — −30° C. 6100    6300 — — 6200    Noack Evaporation 250° C. × 1 h % by mass 9  7.3  7.3 7 9  Amount Noise — dB 75.8 74.9 74.8 74.5 75.5 Fuel Saving — Nm 21.1 21.1 21.3 21.7 19.8 Performance Fatigue Life L50 — minutes 152   158 165   172 160   Comparative Example 1 2 3 4 5 6 7 SAE Viscosity Classification of Composition 15W-30 5W-20 10W-30 10W-40 20 30 40 Composition Base Oil Base Oil-1 35 5 15 (% by mass) Base Oil-2 54.7 Base Oil-3 86.7 78.7 65.6 48 Base Oil-4 41.7 89.7 72.85 Base Oil-5 16.85 Copolymer Copolymer-1 Copolymer-2 3 Polymeric Polymeric Compound-1 Compound Polymeric Compound-2 6 9.1 Additive Pour Point Depressant 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Friction Modifier DI Agent 10 10 10 10 10 10 10 Property of Viscosity Index — — 104 133 104 107 106 107 105 Base oil Noack Evaporation 250° C. × 1 h % by mass 14 9 14 14 9 4 3 Amount Performance Kinematic  40° C. mm²/s 60.72 44.35 68.41 87.46 56.53 97.34 124.7 and Property Viscosity 100° C. 9.104 7.647 10.49 13.17 7.993 11.49 13.57 of Viscosity Index — — 128 141 140 151 108 105 105 Composition HTHS Viscosity 150° C. mPa · s 3.1 2.6 3.1 3.9 2.7 3.5 4.1 Viscosity Reduction 150° C. % — — 11 15.5 — — — Percentage CCS Viscosity −25° C. mPa · s 7800 6300 — — — — — −30° C. — — 5950 6300 — — — Noack Evaporation 250° C. × 1 h % by mass 14.5 9 13.9 13.5 9.2 3.3 3 Amount Noise — dB 74.5 78.3 77.6 75.8 78.5 75.5 74.8 Fuel Saving — Nm 21.9 21.1 21.7 22.2 21.2 21.9 22.4 Performance Fatigue Life L50 — minutes 152 110 149 172 95 148 168

The following points will be understood from the results shown in Table 1:

(1) All of the lubricant oil compositions for internal combustion engines according to the present invention show good noise reducing property, fatigue resistance life, fuel saving performance, evaporation resistance and low viscosity reduction tendency (Examples 1 to 5). In contrast thereto, at least one of these performances is not achievable in the compositions which do not satisfy at least one of the requirements of the present invention. (2) More specifically, the following points are apparent: (i) The compositions of Examples 1, 2 and 5 which have a viscosity grade classified in 5W-20 oil show noise reduction property, fatigue resistance life and evaporation resistance that are comparative to or better than those of the composition of Comparative Example 3 which has a viscosity grade classified in 10W-30 and which has a high viscosity (kinematic viscosity); (ii) The composition of Example 3 which has a viscosity grade classified in 10W-20 oil shows noise reduction property and fatigue resistance life that are comparative to or better than those of the composition of Comparative Example 7 which has a viscosity grade classified in 40 and which has a high viscosity (kinematic viscosity); and (iii) The composition of Example 4 which has a viscosity grade classified in 10W-30 oil shows noise reduction property, fatigue resistance life and evaporation resistance that are comparative to or better than those of the composition of Comparative Example 4 which has a viscosity grade classified in 10W-40 and which has a high viscosity (kinematic viscosity).

INDUSTRIAL APPLICABILITY

The lubricant oil composition for internal combustion engines according to the present invention can provide a lubricant oil composition for internal combustion engines which can, despite of its low viscosity, reduce noise during running, prevent fatigue damage such as gear pitting, reduce the consumption of the oil, and provide excellent fuel saving performance. Accordingly, the present composition maybe suitably used as lubricant oil composition for internal combustion engines that can be suitably utilized as a lubricating oil for four-cycle engines for motorcycles. 

1. A lubricant oil composition, comprising: a base oil having a viscosity index of 125 or higher and a Noack evaporation amount (250° C.×1 h) of 15% by mass or less; and from 0.1 to 10% by mass, based on a total amount of the composition, of (A) a C₂ to C₂₀ olefin polymer having a mass average molecular weight of 500 or more and 10,000 or less, (B) a polymeric compound having a mass average molecular weight of 10,000 or more and less than 100,000, or (A) and (B), wherein a content of (C) a polymeric compound having a mass average molecular weight of 100,000 or more is less than 1.0% by mass.
 2. The composition of claim 1, comprising at least one polymeric compound (B) selected from the group consisting of a polymethacrylate, an olefin copolymer, a styrene copolymer, and a polyisobutylene.
 3. The composition of for claim 1, further comprising a molybdenum-based friction modifier or an ashless friction modifier.
 4. The composition of claim 1, wherein the Noack evaporation amount (250° C.×1 h) of the base oil is 10.0% by mass or less and the viscosity index of the base oil is 140 or higher.
 5. The composition of claim 1, which is suitable for a four-cycle engine in a motorcycle.
 6. The composition of claim 1, wherein the polymeric compound (C) is at least one selected from the group consisting of a polymethacrylate, an olefin copolymer, a styrene copolymer, and a polyisobutylene.
 7. The composition of claim 1, comprising the C₂ to C₂₀ olefin polymer (A).
 8. The composition of claim 1, comprising the polymeric compound (B).
 9. The composition of claim 1, comprising the C₂ to C₂₀ olefin polymer (A) and the polymeric compound (B).
 10. The composition of claim 2, further comprising a molybdenum-based friction modifier or an ashless friction modifier.
 11. The composition of claim 3, comprising the molybdenum-based friction modifier.
 12. The composition of claim 3, comprising the ashless friction modifier.
 13. The composition of claim 10, comprising the molybdenum-based friction modifier.
 14. The composition of claim 10, comprising the ashless friction modifier.
 15. The composition of claim 2, wherein the Noack evaporation amount (250° C.×1 h) of the base oil is 10.0% by mass or less and the viscosity index of the base oil is 140 or higher.
 16. The composition of claim 3, wherein the Noack evaporation amount (250° C.×1 h) of the base oil is 10.0% by mass or less and the viscosity index of the base oil is 140 or higher. 